Inference: The Process

Inference is a mental process by which we reach a conclusion
based on specific evidence. Inferences
are the stock and trade of detectives examining clues, of doctors diagnosing
diseases, and of car mechanics repairing engine problems. We infer motives,
purpose,
and intentions.

Inference is essential to, and part of, being human. We
engage in inference every day. We
interpret actions to be examples of behavior characteristics, intents, or
expressions of particular feelings. We infer it is raining when we see someone
with an open umbrella. We infer people
are thirsty if they ask for a glass of water. We infer that evidence in a text
is authoritative when it is attributed
to a scholar in the field.

We want to find significance. We listen to remarks, and want
to make sense of them. What might the
speaker mean? Why is he or she saying
that? We go beyond specific remarks to
underlying significance or broader meaning. When we read that someone cheated
on
his or her income taxes, we might
take that as an example of financial ingenuity, daring, or stupidity. We
seek purposes and reasons.

Inferences are not random. While they may come about mysteriously with a sudden
jump of
recognition, a sense of "Ah ha!," inferences are very orderly.
Inferences may be guesses, but they are educated guesses based on supporting
evidence.The evidence seems to require
that we reach a specific conclusion.

Evidence is said toimply;
readersinfer. While this image
suggests an intent or power on the part of evidence that does not exist—how,
after all, can a fact compel a certain conclusion?—the image and resulting
terminology are useful nonetheless. The
sense of inevitability to the conclusion suggests that we did not jump to that
conclusion or make it up on our own, but found it by reasoning from the
evidence.

The above image implies that everyone will reach the same
conclusion. That obviously is not the case—as the examples above suggest. The
umbrella might be protection from the
sun, the request for water might indicate a need to take a pill, and a footnote
may cite only one side of a controversy. Here again, the line between
inference and jumping to a conclusion can
be awfully thin.

A man gets on a bus. What
might be implied by each of the following?

He ran to catch the bus.

He is carrying a suitcase.

He asks the driver for change of a $100 bill.

Inferences are not achieved with mathematical rigor. Inferences do not have
the certainty obtained with deductive reasoning. Inferences tend to
reflect prior knowledge
and experience as well as personal beliefs and assumptions. Inferences thus
tend to reflect one's stake
in a situation or one's interests in the outcome. People may reason differently
or bring different assumptions or premises to bear.

Given evidence that PCB's
cause cancer in people, and that PCB's
are in a particular water system, all reasonable people would reach the
conclusion that that water system is dangerous to people. But given evidence
that
there is an increase in skin cancer among people who sun bathe, not all people
would conclude that sunbathing causes skin cancer. Sun bathing, they might
argue, may be coincidental with exposure
to other cancer causing factors.

More often than not, disagreements
are based not on differences in reasoning, but in the values, assumptions, or
information brought to bear. If we
believe that all politicians are crooks, we will infer that a specific
politician's actions are scurrilous. If
we believe that politicians act for the good of all, we will look for some
benefit in their actions. Either way,
we will try to use reason to explain the actions. We will look for some
coherent explanation as a way of making
sense of things. As we saw earlier, if
we can understand why someone would do something, why someone might say
something, why someone might act in a certain way, we feel we have made sense
of the act or statement. It's like a murder trial: if we can put together
opportunity, motive, and means, we can make a case.

The more evidence we have before us, and the more carefully
we reason, the more valid our inferences. This principle plays an important
role with reading: the more evidence
within a text we incorporate into our interpretation, the more likely we have
not gone astray from any intended meaning.